Function Block binding in Rust 1.55

Block binding in Rust allows variables to be explicitly bound and scoped within a block of code. This means that a variable can be defined and assigned a value within a block and will not be accessible outside of that block.

The syntax for block binding is to use the let keyword followed by the variable name and its value, enclosed in curly braces.

Here are a few examples of block binding in Rust:

## Example 1

fn main() {
    let x = 5;
    
    {
        let y = 10;
        println!("x: {}, y: {}", x, y);
    }
    
    println!("x: {}", x);
}

In this example, we first define a variable x and assign it the value of 5. We then create a block using curly braces and define a variable y with a value of 10. We can access both x and y within the block and print their values.

However, outside of the block, we can only access x since y was defined within the block and is not accessible outside of it.

The output of this example will be:

x: 5, y: 10
x: 5

## Example 2

fn main() {
    let x = 5;
    
    {
        let x = 10;
        println!("x: {}", x);
    }
    
    println!("x: {}", x);
}

In this example, we define a variable x with a value of 5 and create a block. Within the block, we define another variable x with a value of 10. This creates a new binding for x within the block, which shadows the outer x.

When we print the value of x within the block, it will be 10 due to the new binding. When we print the value of x outside of the block, it will be 5 since the outer x was not affected by the inner binding.

The output of this example will be:

x: 10
x: 5

## Example 3

fn main() {
    let x = 5;
    let y = {
        let x = 10;
        x + 5
    };
    
    println!("x: {}, y: {}", x, y);
}

In this example, we define a variable x with a value of 5. We then define a block and assign its value to y. Within the block, we define a new binding for x with a value of 10. We then add 5 to x and return the result, which becomes the value of y.

When we print the values of x and y, we can see that x is still 5 since the inner binding did not affect the outer x. The value of y is 15, which is the result of adding 10 and 5 within the inner block.

The output of this example will be:

x: 5, y: 15